Aluminum alloy with improved extrudability and corrosion resistance

ABSTRACT

There is provided an extruded and brazed product with improved corrosion resistance by having low coarse recrystallized grain formation as well as a method for making same. The extruded and brazed product comprises an aluminum alloy comprising in weight percent Mn 0.6-0.75; Fe 0.11-0.16; Si 0.10-0.19; Cu&lt;0.01; Zn&lt;0.05; Ti&lt;0.05; optionally a grain refiner; optionally Ni&lt;0.01; and the balance being aluminum and inevitable impurities.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from U.S. provisional patentapplication 62/925,314 filed on Oct. 24, 2019 and herewith incorporatedin its entirety.

TECHNICAL FIELD

The present disclosure relates to aluminum alloy-based extruded andbrazed products and methods for producing same.

BACKGROUND OF THE ART

Aluminum alloys provide corrosion resistance to manufactured parts, andare used for example in the automotive industry as well as in heatexchangers and air conditioning applications. They are used in tubingbecause of their good extrudability while being light weight andoffering moderate strength. Long-life corrosion resistant alloys havetypically used high Mn contents or additions of Ti, which aredetrimental to extrudability and can reduce extrusion speeds and dielife. It is a challenge to improve extrudability without hindering thelong-life corrosion performance of the alloys. Improvements are desired.

SUMMARY

The present disclosure concern aluminum alloy having increasingextrudability characteristics as well as aluminum products comprisingsame having increased corrosion resistance.

In a first aspect, the present disclosure provides an extruded andbrazed product comprising an aluminum alloy comprising in weight percentMn 0.6-0.75; Fe 0.11-0.16; Si 0.10-0.19; Cu<0.01; Zn<0.05; Ti<0.05 withthe balance being aluminum and inevitable impurities. In the extrudedand brazed product, less than 15% of the product's width includes coarserecrystallized grains. In an embodiment, each of the inevitableimpurities is present at a maximum of 0.03 and the total inevitableimpurities comprises less than 0.10. In another embodiment, the aluminumalloy comprises less than 0.01 Ni. In still another embodiment, thealuminum alloy comprises less than 0.05 Mg. In still a furtherembodiment, the aluminum alloy comprises less than 0.05 Cr. In yetanother embodiment, the aluminum alloy comprises between 0.64 to 0.72Mn. In still a further embodiment, the aluminum alloy comprises between0.11 to 0.14 Si. In some embodiments, the aluminum alloy comprisesbetween 0.12 to 0.16 Fe. In additional embodiments, the aluminum alloycomprises between 0.011 to 0.024 Ti. In some embodiments, the extrudedand brazed product is an extruded and brazed tubing, such as, forexample, a micro-multiport tubing.

In another aspect, the present disclosure provides a method forproducing an extruded and brazed product. First, a billet is provided,the billet comprising an aluminum alloy comprising in weight percent Mn0.6-0.75; Fe 0.11-0.16; Si 0.10-0.19; Cu<0.01; Zn<0.05; Ti<0.05 with thebalance being aluminum and inevitable impurities. Then, the billet ishomogenized with at least one heat treatment. The billets are thenextruded into the product and the product is brazed to obtain theextruded and brazed product. The method can further comprise, beforeproviding the billets, casting the aluminum alloy into the billets. Inan embodiment, the method further comprises, after homogenizing andbefore extruding, cooling the billets. In an embodiment, each of theinevitable impurities of the aluminum alloy is present at a maximum of0.03 and the total inevitable impurities comprises less than 0.10. In anembodiment, the aluminum alloy comprises less than 0.01 Ni. In anotherembodiment, the aluminum alloy comprises less than 0.05 Mg. In a furtherembodiment, the aluminum alloy comprises less than 0.05 Cr. In still afurther embodiment, the aluminum alloy comprises between 0.64 to 0.72Mn. In still another embodiment, the aluminum alloy comprises between0.10 to 0.14 Si. In yet another embodiment, the aluminum alloy comprisesbetween 0.12 to 0.16 Fe. In still another embodiment, the aluminum alloycomprises between 0.011 to 0.024 Ti. In an embodiment, the extruded andbrazed product is a tubing, such as, for example, a micro-multiporttubing.

In a third aspect, the present disclosure provides an extruded andbrazed product obtainable or obtained by the method described herein.

Many further features and combinations thereof concerning the presentimprovements will appear to those skilled in the art following a readingof the instant disclosure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of dispersoid volume fraction of three aluminum alloycompositions (content in Fe and Si is provided in the figure legend) asa function of soak time (hours).

FIG. 2 is an example of standard alloy AA3012A exhibiting coarserecrystallized grains through the outer wall thickness.

FIG. 3 shows the surface of sample in FIG. 2 after macroetching showingcoarse recrystallized grains on surface.

FIG. 4A shows the surface grain structure revealed by Poulton'smacrotech of different tubes obtained from a commercial operation. Thematerial on the left is the “as extruded” tube, the material in themiddle has been submitted to a simulated braze thermal cycle of 2 min.at 605° C. whereas the material on the right has been submitted to asimulated braze thermal cycle of 4 min. at 605°.

FIG. 4B shows the surface grain structure revealed by Poulton'smacrotech of brazed tubes obtained from a commercial operation. Thematerial has been submitted to a simulated braze thermal cycle of 4 min.at 625°.

DETAILED DESCRIPTION

The present disclosure concerns Al—Mn—Si—Fe extrusion alloys havingimproved extrudability as well as products comprising same exhibitinglong-life corrosion resistance. The aluminum alloys of the presentdisclosure exhibit improved extrudability. The extruded and brazedproducts made from the alloys of the present disclosure exhibit a finepost-brazed grain structure and/or tolerance to extended homogenizationand brazing cycles. As used in the context of the present disclosure, a“fine post-brazed grain structure” refers to a structure consistingmainly of residual fine grains produced during the extrusion process andthe corresponding absence of coarse recrystallized grains formed duringthe braze cycle. The expression “fine as-extruded grain structure”refers to the a structure consisting mainly of residual fine grainsproduced during the extrusion process and before any brazing cycle.Still according to the present disclosure, the term “coarserecrystallized grains” refers to grains with a width across the extrudedsurface (i.e. perpendicular to the extrusion direction) higher than 200microns or grains with a thickness extending through the entire outerwall thickness of the tube. FIG. 2 shows an example of the grainstructure of alloy AA3012A after sizing and brazing where coarserecrystallized grains are present extending through the wall thickness.FIG. 3 shows the appearance of the tube surface of the same sample as inFIG. 2 after macroetching, revealing coarse recrystallized grains on thetube surface with a width higher than 200 microns.

The alloys of the present disclosure are especially useful in makingextruded (e.g., aluminum) products. “Extruded aluminum products” refersto products made from the aluminum alloy of the present disclosure whichhave been pushed through a die at elevated temperature to obtain adesired cross section.

The extruded aluminum products of the present disclosure are brazed toother components, for example to create a heat exchanger. “Brazing” asdefined herein is the process of metal-joining two or more items bymelting and flowing a filler metal into at least one joint. A “brazedproduct” is defined as having been subjected to brazing.

As indicated herein, the chemistry of the aluminum alloys of the presentdisclosure favors retention of a fine post-brazed grain structure in theouter wall of the product (e.g., tube) and thus prevents or limitsrecrystallization or “coarse grain formation” during high temperaturebrazing. Recrystallization at this stage replaces the desirable finegrain structures resulting from extrusion and replaces it with a coarsegrain structure where one coarse grain can occupy the entire tube wallthickness. This condition offers a direct corrosion path through thematerial and is detrimental to the corrosion resistance of the tubing.Thus, recrystallization into coarser grains has to be avoided, preventedor limited.

In a first aspect, there is provided an aluminum alloy comprising inweight percent Mn about 0.6 to about 0.75; Fe about 0.11 to about 0.16;Si about 0.10 to about 0.19; Cu less than about 0.01; Zn less than about0.05; Ti less than about 0.05; optionally a grain refiner; optionally Niless than about 0.01; and the balance being aluminum and inevitableimpurities.

The aluminum alloy of the present disclosure is an Al—Mn—Si—Fe alloy andthus includes Mn. However, the Mn content of the aluminum alloy of thepresent disclosure is lower than standard corresponding “long-life”Al—Mn—Si—Fe alloys. This reduction in Mn content provides reduced flowstress and improved extrudability. Mn is also important for theformation of Al—Mn—Fe—Si dispersoids and for providing increasedself-corrosion protection along with adequate mechanical strength. Mncan be present in the aluminum alloy of the present disclosure in weightpercent from about 0.6 to about 0.75, from about 0.61 to about 0.74,from about 0.62 to about 0.73, from about 0.63 to about 0.72, from about0.64 to about 0.71, from about 0.65 to about 0.70, from about 0.66 toabout 0.69, from about 0.67 to about 0.68, from about 0.6 to about 0.74,from about 0.6 to about 0.73, from about 0.6 to about 0.72, from about0.6 to about 0.71, from about 0.6 to about 0.70, from about 0.6 to about0.69, from about 0.6 to about 0.68, from about 0.6 to about 0.67, fromabout 0.6 to about 0.66, from about 0.6 to about 0.65, from about 0.6 toabout 0.64, from about 0.6 to about 0.63, from about 0.6 to about 0.62,from about 0.6 to about 0.61, from about 0.61 to about 0.75, from about0.62 to about 0.75, from about 0.63 to about 0.75, from about 0.64 toabout 0.75, from about 0.65 to about 0.75, from about 0.66 to about0.75, from about 0.67 to about 0.75, from about 0.68 to about 0.75, fromabout 0.69 to about 0.75, from about 0.70 to about 0.75, from about 0.71to about 0.75, from about 0.72 to about 0.75, from about 0.73 to about0.75, from about 0.74 to about 0.75 or from about 0.64 to 0.72.

The aluminum alloys of the present disclosure also include Fe which isbeneficial for increasing the resistance to coarse recrystallized grainformation after homogenization. Fe also plays a role in controlling thedistribution of Al—Mn—Fe—Si dispersoids. Furthermore, Fe reduces thesolubility of Mn and facilitates the formation of Al—Mn—Fe—Sidispersoids. However, excessive levels of Fe can be detrimental topitting corrosion resistance by providing active cathode sites. Fe canbe present in the aluminum alloy of the present disclosure in weightpercent from about 0.11 to about 0.16, from about 0.12 to about 0.15,from about 0.13 to about 0.14, from about 0.12 to about 0.16, from about0.13 to about 0.16, from about 0.14 to about 0.16, from about 0.15 toabout 0.16, from about 0.11 to about 0.15, from about 0.11 to about0.14, from about 0.11 to about 0.13 or from about 0.11 to about 0.12.

The Si present in the aluminum alloys of the present disclosure promotesAl—Mn—Fe—Si dispersoid formation and contributes to the distribution ofthe Al—Mn—Fe—Si dispersoids. In addition, Si reduces the tendency forreduction in the volume fraction of dispersoids with extendedhomogenization times. As shown in the Examples, it was surprisinglyfound that Si provided remarkable control of the post-brazed grain sizestructure control under severe processing conditions to obtain desirablelow recrystallization. However, excessive Si levels can lower the bulkmelting point of the alloy and reduce extrudability. Si can be presentin the aluminum alloys of the present disclosure in weight percent fromabout 0.10 to about 0.19, from about 0.11 to about 0.19, from about 0.12to about 0.19, from about 0.13 to about 0.19, from about 0.14 to about0.19, from about 0.15 to about 0.19, from about 0.16 to about 0.19, fromabout 0.17 to about 0.19, from about 0.18 to about 0.19, from about 0.10to about 0.18, from about 0.11 to about 0.18, from about 0.12 to about0.18, from about 0.13 to about 0.18, from about 0.14 to about 0.18, fromabout 0.15 to about 0.18, from about 0.16 to about 0.18, from about 0.17to about 0.18, from about 0.10 to about 0.17, from about 0.11 to about0.17, from about 0.12 to about 0.17, from about 0.13 to about 0.17, fromabout 0.14 to about 0.17, from about 0.15 to about 0.17, from about 0.16to about 0.17, from about 0.10 to about 0.16, from about 0.11 to about0.16, from about 0.12 to about 0.16, from about 0.13 to about 0.16, fromabout 0.14 to about 0.16, from about 0.15 to about 0.16, from about 0.10to about 0.15, from about 0.11 to about 0.15, from about 0.12 to about0.15, from about 0.13 to about 0.15, from about 0.14 to about 0.15, fromabout 0.10 to about 0.14, from about 0.11 to about 0.14, from about 0.12to about 0.14, from about 0.13 to about 0.14, from about 0.10 to about0.13, from about 0.11 to about 0.13, from about 0.12 to about 0.13, fromabout 0.10 to about 0.12, from about 0.11 to about 0.12, from about 0.10to about 0.11.

The aluminum alloys of the present disclosure can include, in someembodiment, Cu. However, if present, the Cu content is limited to lessthan 0.01 wt. % as it can reduceself-corrosion resistance.

The aluminum alloys of the present disclosure can include, in someembodiments, Zn. Extruded tubes for heat transfer applications arefrequently coated with a galvanically sacrificial layer of Zn. The Znmay be deposited by arc spray, use of a Zn containing flux or by plasmaspray and the Zn diffuses into the tube surface during heating to thebraze temperature. The Zn concentration in the base alloy is limited toless than 0.05 wt. % as it can interfere with the behaviour of thesacrificial coating if present in a higher concentration. A grainrefiner may be optionally included in the aluminum alloys of the presentdisclosure to solidify aluminum alloys with a fully equiaxed, fine grainstructure, in the form of Ti, TiB or TiC. When TiB is used as a grainrefiner, this may result in a B content of up to 0.01 wt. % in thealloy.

The aluminum alloys of the present disclosure can include, in someembodiments, Ti. However, a high content of Ti can be detrimental toextrudability and can reduce extrusion speeds and die life, thereforethe concentration of Ti, if present, is limited to less than 0.05 wt. %.For example in weight percent less than about 0.030, less than about0.027 or less than about 0.024. As indicated above, it may be desirableto add low levels of Ti to extrusion alloys as a grain refiner duringcasting either as Ti or combined with B as a TiB grain refiner or with Cas a TiC grain refiner.

The aluminum alloys of the present disclosure can include, in someembodiments, Ni. However, since Ni can reduceself-corrosion resistance,the content of Ni is less than 0.01.

In the aluminum alloys of the present disclosure, Mg is optionallypresent but is kept relatively low for extrudability and brazeability ofthe alloy, less than 0.05 wt %.

In some embodiments, the balance of the alloy includes aluminum andinevitable impurities. In some embodiments, each of the inevitableimpurity is present at a maximum of 0.05 (and in some embodiments 0.03)and the total inevitable impurities comprises less than 0.10.

The extruded and brazed product of the present disclosure includeAl—Mn—Fe—Si dispersoids. The Al—Mn—Fe—Si dispersoids are submicronparticles that play a role in the deformation behaviour,recrystallization behaviour and resulting mechanical properties ofproducts comprising the aluminum alloys of the present disclosure. Insome embodiments, the dispersoids allow the fine as-extruded grainstructure to be retained in the outer wall of a tube, after typical coldsizing and brazing treatments, for example combining the tubing withfins and header tubes to make a brazed heat exchanger. Without wishingto be bound to theory, the retention of the fine as-extruded grainstructure in the outer wall of the shape, after brazing, contributes tothe corrosion resistance by presenting a more tortuous corrosion paththrough walls of the shape.

In an embodiment, the extruded and brazed products include less than 15%coarse recrystallized grains across the tube width, preferably less than12%, most preferably less than 10% when subjected to severe brazingand/or less than 5% recrystallization, preferably less than 3%, mostpreferably less than 1% when subjected to standard brazing (such as, forexample, standard controlled atmosphere (CAB) brazing). The percentagereferring to the percentage of the outer tube wall consisting of coarserecrystallized grains. In an embodiment, less than 15%, 14%, 13%, 12%,11% or 10% of the extruded and brazed product width is occupied bycoarse recrystallized grains when subjected to severe brazing and/orless than 5%, 4%, 3%, 2% or 1% recrystallization when subjected tostandard controlled atmosphere (CAB) brazing which is widely used forthe production of aluminum heat exchangers. The percentage referring tothe percentage of the outer tube wall width consisting of coarserecrystallized grains.

The extruded and brazed products can be provided in any shape or form.In some embodiments, the extruded and brazed products can be in the formof a tube or a plurality of tubes. In some specific embodiments, theextruded and brazed products can be or comprise micro-multiport tubing(MMP). When the extruded and brazed products are tubing or tubes (suchas MMP), they can have a wall thickness of equal to or less than about0.4 mm, 0.3 mm or 0.2 mm.

The present disclosure also provides a method for producing extruded andbrazed products. The method comprises working the aluminum alloy of thepresent disclosure into the aluminum product. The working step caninclude casting the aluminum alloy directly into an intermediary billetintended for extrusion.

In some embodiments, methods of the present disclosure first providesbillets comprising an aluminum alloy as described herein. Then, thebillets are homogenized with at least one heat treatment, the heattreatment comprising a treatment temperature in the range of 540° C. to590° C. and for at least one soak time ranging from 1 to 8 hours toobtain an homogenized aluminum alloy billet. Next, the billets areextruded into products such as tubing. The product (tubing) is thenoptionally coiled, uncoiled, cold sized, assembled and then brazed toobtain the brazed product (tubes forming part of a heat exchanger). Thebrazing step can comprise at least one brazing cycle.

In one embodiment of the method, before providing the billets, thealuminum alloy of the present disclosure is cast into the billets. Inone embodiment of the method, after homogenizing and before brazing, thehomogenized aluminum products are cooled down, preferably at a coolingrate of 300° C./h or less.

EXAMPLE I Effect of Mn and Fe on Recrystallization of Brazed Tubes

The alloys A to E (chemistry detailed in Table 1) were direct chill (DC)cast as 101 mm billets. Alloy A represents the existing state of theart, and is the benchmark of comparison. The concentration of Mn in theexperimental alloys was increased compared to alloy A, alloys B and Chad 0.64 wt. % Mn, and alloys D and E had 0.70 wt. % Mn. Theconcentration of Fe was increased compared to alloy A only in alloys Cand E, to 0.14 and 0.15 wt. % respectively.

TABLE 1 The compositions of alloys A to E in weight percent, the balancebeing Al and inevitable impurities Alloy Cu Fe Mn Ni Si Ti Zn A 0.0010.10 0.60 0.006 0.10 0.020 0.003 B 0.002 0.10 0.64 0.008 0.10 0.0150.004 C 0.002 0.14 0.64 0.004 0.10 0.017 0.017 D 0.002 0.10 0.70 0.0080.10 0.015 0.004 E 0.002 0.15 0.70 0.008 0.10 0.015 0.004

The billets B to E were homogenized using four treatments, the firsttreatment (TR1) was 2 h at 550° C., the second treatment (TR2) was 6 hat 550° C., the third treatment (TR3) was 2 h at 560° C., and the fourthtreatment (TR4) was 6 h at 560° C. Billet A was only homogenized withTR1 and TR2. The billets were then cooled at 300° C./h. The cooledmaterial was then extruded into mini microport (MMP) tubing with anouter wall thickness of 0.35 mm using a billet temperature of 480° C.and an exit speed of 77 m/min. Lengths of the tubing were cold sized byrolling to give a thickness reduction of 4% to replicate commercial tubesizing. Simulated brazing cycles of 2.5 min at 605° C. (cycle 1) and625° C. (cycle 2) were then applied, and the grain structures wereassessed by macro-etching the external flat surface of the tube andmeasuring the proportion of the tube width occupied by coarserecrystallized grains, where the term “coarse grains” refers to grainswith a width on the extruded surface >200 microns or grains with athickness extending through the entire wall thickness The results areshown in Table 2.

TABLE 2 Results (in percentage) of tube width occupied by coarserecrystallized grains for alloys A to E Braze cycle 1 Braze cycle 2Alloy TR1 TR2 TR3 TR4 TR1 TR2 TR3 TR4 A 0 10 50 60 B 0 0 0 0 50 10 62 4C 0 0 0 0 0 5 13 3 D 0 0 0 0 13 5 38 50 E 0 0 0 0 0 5 13 16

The extent of undesirable coarse recrystallized grains increased withincreasing homogenization soak time/temperature, and increasing brazetemperature. Alloy A retained a fine grain structure when homogenisedfor 2 hrs/550° C. and brazed at 605° C. However, it gave significantrecrystallization when the soak time was increased to 6 hours of soak at550° C., and 605° C. braze. Increasing the braze temperature to 625° C.gave excessive recrystallization for both soak times. Thereforevariations in braze temperature and homogenization soak time, which arepossible in commercial operations, could result in excessive coarserecrystallized grain when using alloy A.

Under the experimental conditions tested, acceptable targets for coarserecrystallized grain formation are zero coarse recrystallized grainformation with the standard brazing treatment at 605° C. and <15% afterthe more severe treatment at 625° C. The latter represents formation ofsingle coarse recrystallized grains at the tube nose (ends) where thestrain is more concentrated during sizing. In this example, Alloy Bperformed slightly better than alloy A, in terms of coarserecrystallized grain formation. However, the performance, when brazed at625° C., was unacceptable for homogenization temperatures in the rangeof 550 to 560° C. Alloy C gave significantly better resistance to coarserecrystallized grain formation along with Alloy E, suggesting thatincreasing the Fe content is beneficial. Alloy D, with an increased Mncontent compared to alloy B but the same Fe content, gave unacceptablebehaviour at the higher braze temperature, suggesting that increasingthe Mn content alone is not sufficient to prevent coarse recrystallizedgrain formation.

EXAMPLE II Effect of Si on Recrystallization of Brazed Tubes

The alloys A, F, G and H (chemistry detailed in Table 3) were DC cast as101 mm diameter billets. Alloy A represents the existing state of theart, and is the benchmark of comparison. Alloys F, G, H had increasingconcentrations of Si 0.08, 0.14, and 0.19 wt. % respectively.

TABLE 3 The compositions of alloys A, F, G and H in weight percent thebalance being Al and inevitable impurities Alloy Cu Fe Mn Ni Si Ti Zn A0.001 0.10 0.60 0.006 0.10 0.020 0.003 F 0.002 0.12 0.59 0.005 0.080.022 0.007 G 0.002 0.12 0.59 0.005 0.14 0.020 0.007 H 0.002 0.12 0.600.005 0.19 0.025 0.007

The alloys were homogenized for 6 h at 580° C. to represent a hightemperature long-soak cycle. The billets were then cooled at 300° C./h.The cooled material was then extruded into mini microport (MMP) tubingwith an outer wall thickness of 0.35 mm using a billet temperature of480° C. and an exit speed of 77 m/min. Lengths of the tubing were coldrolled to give thickness reductions of 4% to replicate commercial tubesizing, and 10% to investigate excessive sizing. Then an extreme brazecycle of 2.5 min at 625° C. was applied. The grain structures wereassessed by macro-etching the flat surface of the tube and measuring theproportion of the tube width occupied by coarse recrystallized grains.The results are shown in Table 4.

TABLE 4 Results (in percentage) of proportion of tube width occupied bycoarse recrystallized for alloys A, F, G and H. Alloy 4% thicknessreduction 10% thickness reduction A 100 100 F 100 100 G 10 10 H 0 10

As expected, alloy F, which has a similar composition to alloy A butwith an increased Fe content, fully recrystallized to a coarse grainstructure. However, increasing the Si from 0.08 to 0.14 wt. %, in alloyG, provided remarkable control of the post-brazed grain size, and thetrend continued with alloy H with 0.19 wt. % Si. Therefore, slightincreases in Si content can provide post-brazed grain structure controlunder severe processing conditions. Increasing the Si content from 0.08to 0.19 reduces the melting point by 4° C., which could have some impacton extrudability. Therefore, further increases in Si beyond 0.19 wt. %are undesirable

EXAMPLE III Al—Mn—Fe—Si Dispersoid Modeling

Without wishing to be bound to theory, the mechanism of controlling thepost-brazed structure and preventing coarse recrystallized grainrecrystallization seems to be due, at least in part, to grain boundarypinning by submicron alpha-Al—Mn—Fe—Si dispersoid particles, which arepresumed to form during homogenization. The pinning effect isproportional to the volume fraction/particle radius. The effects ofcomposition and homogenization cycle observed in these experiments wereprobably due to changes in these two parameters. Using a proprietaryhomogenization model developed to predict dispersoid growth and solutediffusion across a dendrite arm, it is possible to predict the effectsof composition on the dispersoid distribution. FIG. 1 shows how thevolume fraction of dispersoids varies with Fe and Si contents for a 0.70wt.% Mn base alloy during homogenization at 550° C. With a base level of0.08 wt. % Si, increasing Fe from 0.10 to 0.15 wt. % increased thevolume fraction, but this starts to reduce after 2-3 hours soak, meaningthat extended homogenization times can reduce the ability to preventcoarse recrystallized grain formation. When the Si content is increasedfrom 0.08 to 0.13 wt. the initial dispersoid volume fraction is lowerbut continues to increase with longer homogenization times. This canoffset the effect of extended soaking, which can occur under productionconditions.

EXAMPLE IV Corrosion Resistance Test

Alloys A, B, C, D, E, F, G and H were homogenised as described above andextruded into a 30×1.4 mm strip using a billet temperature of 480° C.and an exit speed of 75 m/min. Commercial alloy variants correspondingto AA3102 and an established commercial long life alloy were alsoprocessed for comparison. The material was water quenched at the dieexit. A simulated braze cycle of 5 mins at 605° C. was applied to 100 mmcoupons. These were degreased in alcohol and then 4 coupons per alloyexposed in the SWAAT corrosion test (ASTM G85) for 20 days. The mean pitdepth was measured for each sample based on the 6 deepest pits percoupon selected by eye. The results after 20 days exposure in theaccelerated corrosion test are shown in Table 5. A low pit depth isdesirable and is an indicator of superior resistance to pittingcorrosion in service. The established commercial long life alloy, basedon AA3012A, performed the best in SWAAT but the experimental alloys B-E,including the inventive alloys C, E, G and H all performed better thanthe state of the art alloys A and F and the standard commercial alloyAA3102

TABLE 5 SWAAT Test Results Alloy Pit depth at 20 days (μ) A 441 B 379 C390 D 387 E 404 F 435 G 406 H 328 Established commercial alloy 293AA3102 676

EXAMPLE V Flow Stress Test

The extrudability, or potential extrusion speed of Al—Mn type alloys iscontrolled by the alloy flow stress at elevated temperature. A lowerflow stress is an indicator of potentially higher extrusion speed andreduced die wear. Billets of alloys C and E were homogenized to a cycleof 2 hrs/550° C. followed by cooling at 250° C./hr and alloys F, G and Hwere homogenised to a cycle of 2 hrs/580° C. followed by cooling at 250°C./hr. A sample of the established commercial long life alloy was alsoprocessed to a standard commercial practice. Cylindrical samples 10 mmdia. x 10 mm in length were machined. Triplicate samples were tested inhot compression using a Gleeble 3800 machine. The samples were heated at100° C./min to 450° C. and held for 5 mins before deforming incompression at a strain rate of 1/sec to a strain of 0.8. The recordedload was converted to true stress and the value at a strain of 0.7 wasextracted as a measure of the flow stress. The mean flow stress ofalloys C, E, G and H was 7-10% lower than the existing establishedcommercial long life alloy, corresponding to a significant improvementin extrusion performance in all cases.

TABLE 6 Flow stress measured at 450° C. at a strain rate of 1/s AlloyHomogenisation Flow stress (MPa) C 2 h/550° C. 37.58 E 2 h/550° C. 36.33F 2 h/580° C. 37.34 G 2 h/580° C. 36.76 H 2 h/580° C. 36.62 Establishedcommercial alloy Commercial 40.2

EXAMPLE VI Grain Structure of Brazed Tubes at a Commercial Scale

The alloy composition whose chemistry is detailed Table 7 was directchill (DC) cast as 203 mm diameter billets. The billets were thenhomogenized (4 hrs/550° C.) and cooled (215° C./hr).

TABLE 7 The composition of the alloy used in weight percent, the balancebeing Al and inevitable impurities. Si Fe Cu Mn Ni Zn Ti 0.13 0.13 0.0010.67 0.006 0.002 0.020

The material was extruded into a microchannel tube with a 0.3 mm wall ona commercial extrusion press. The microchannel tube surface was zinc arcsprayed at the press exit prior to passing through a water quench. Thetubing was coiled at the press and then processed through an offlinecut-to-length and sizing operation where a reduction was applied to thetube thickness.

Simulated braze thermal cycles of 2 min. at 605° C., 4 min. 605° C. andan extreme cycle of 4min. 625° C. were applied using a laboratoryfurnace. FIGS. 4A and 4B show the corresponding surface grain structuresas revealed by Poultons macroetch. The “as extruded tube” exhibited onlyfine grain. The post brazed grain structure after all three treatmentswas fine except for a narrow band of coarse grain along one size of thetube. The band width corresponded to 6% of the tube width in all threecases.

As can be seen therefore, the examples described above and illustratedare intended to be exemplary only. The scope is indicated by theappended claims.

1. An extruded and brazed product comprising: an aluminum alloycomprising in weight percent: Mn 0.6-0.75; Fe 0.11-0.16; Si 0.10-0.19;Cu<0.01; Zn<0.05; Ti<0.05; optionally a grain refiner; optionallyNi<0.01; and the balance being aluminum and inevitable impurities;wherein less than 15% of a width of the extruded and brazed tube widthproduct includes coarse recrystallized grains.
 2. The extruded andbrazed product of claim 1, wherein each of the inevitable impurities ispresent at a maximum of 0.05 weight percent and the total inevitableimpurities comprises less than 0.10 weight percent.
 3. The extruded andbrazed product of claim 1, wherein the aluminum alloy comprises inweight percent: less than 0.01 Ni, less than 0.05 Mg, and/or less than0.05 Cr.
 4. The extruded and brazed product of claim 1, wherein thealuminum alloy comprises in weight percent: Fe 0.13-0.16 and Si0.13-0.191.
 5. (canceled)
 6. The extruded and brazed product of claim 1,wherein the aluminum alloy comprises in weight percent 0.64 to 0.72 Mn.7. The extruded and brazed product of claim 1, wherein the aluminumalloy comprises in weight percent 0.10 to 0.14 Si.
 8. The extruded andbrazed product of claim 1, wherein the aluminum alloy comprises inweight percent 0.12 to 0.16 Fe.
 9. The extruded and brazed product ofclaim 1, wherein the aluminum alloy comprises in weight percent 0.011 to0.024 Ti.
 10. The extruded and brazed product of claim 1, wherein theextruded and brazed product is an extruded and brazed tubing.
 11. Theextruded and brazed product of claim 10, wherein the extruded and brazedtubing is or comprises micro-multiport tubing.
 12. A method forproducing the extruded and brazed product of claim 1 comprising: a)providing billets comprising an aluminum alloy comprising in weightpercent: Mn 0.6-0.75; Fe 0.11-0.16; Si 0.10-0.19; Cu<0.01; Zn<0.05; Ti21 0.05; optionally a grain refiner; optionally Ni<0.01; and the balancebeing aluminum and inevitable impurities; b) homogenizing the billetswith at least one heat treatment, the at least one heat treatmentcomprising a treatment temperature in the range of 540° C. to 590° C.for at least one soaking period from 1 to 8 hours to obtain anhomogenized aluminum alloy; c) extruding the billets to obtain anextruded product; and d) brazing the extruded product to obtain theextruded and brazed product.
 13. The method of claim 12, furthercomprising, before providing the billets, casting the aluminum alloyinto the billets.
 14. The method of claim 12, further comprising, afterhomogenizing and before extruding, cooling the billets.
 15. The methodof claim 12, wherein each of the inevitable impurities of the aluminumalloy is present at a maximum of 0.03 weight percent and the totalinevitable impurities comprises less than 0.10 weight percent.
 16. Themethod of claim 12, wherein the aluminum alloy comprises in weightpercent Fe 0.13-0.16, Si 0.13-0.19, less than 0.01 Ni less than 0.05 Mg,and/or less than 0.05 Cr. 17-18. (canceled)
 19. The method of claim 12,wherein the aluminum alloy comprises in weight percent 0.64 to 0.72 Mn.20. The method of claim 12, wherein the aluminum alloy in weight percentbetween 0.10 to 0.14 Si.
 21. The method of claim 12, wherein thealuminum alloy in weight percent between 0.12 to 0.16 Fe.
 22. The methodof claim 12, wherein the aluminum alloy comprises in weight percent0.011 to 0.024 Ti.
 23. The method of claim 12, wherein the extruded andbrazed product is a tubing.
 24. The method of claim 23, wherein thetubing is a micro-multiport tubing.
 25. (canceled)